Commercial refrigerators and freezers, such as ones employed in laboratories, generally comprise a cabinet or compartment having a rectangular opening in one of the vertical walls. A door mounting frame is inserted within this opening, and a plurality of insulated glass doors are hingedly mounted within the frame. Because the insulated glass doors usually comprise a plurality of glass panes, they are relatively heavy and require a sturdy and rugged frame for supporting their weight and for withstanding abusive repeated opening and closing that occurs in laboratory environments.
The normal operating temperature for commercial refrigeration units is between about 34° F. and 36° F., while commercial freezer units may be operated as low as −30° F. or more. If preventative measures are not taken, portions of the metal frame will cool to temperatures below the dew point temperature of the ambient air, resulting in the accumulation of condensation and/or frost on the surface of the frame. Such condensation build up in commercial refrigeration and freezer door assemblies is undesirable since it can create a puddle below the door, which is a safety hazard. It further graphically shows the waste of energy.
To prevent condensation and frost formation on the metal door's mounting frame, it has been the practice to include electrical resistance heating wires within the frame for maintaining the portions of the frame exposed to warmer ambient air at a temperature above the dew point of the ambient air. Such electrical heating means not only adds to the manufacturing cost of the frame, but increases the operating cost of the refrigerator or freezer unit.
While considerable efforts have been directed toward combating condensation build up and minimizing heating requirements, such as by insulating the frame, or interrupting the heat conductive path through the frame by means of thermal barriers or breaks, these efforts have not been entirely successful and often complicate the manufacture of the frame. For example, one approach has been to create a thermal break in the door mounting frame by forming an aluminum extrusion with a channel shaped opening, pouring hot melted plastic material into the opening which solidifies in an intimate contact with the channel, and thereafter severing the channel to separate the frame into independent sections separated by the solid plastic. Such a procedure is highly time consuming, and hence, significantly adds to the manufacturing cost of the product. Proposals to change the material of the frame so that it is less expensive or less heat conductive generally have not been adopted, usually by reason of strength considerations and the desire that the frame have an attractive metal finish consistent with existing commercial freezers and refrigerators.
Notwithstanding the foregoing efforts, a particularly troublesome condensation problem has continued to occur on the metal sealing strip of the door mounting frame, which serves as an attraction and sealing plate for a magnet carrying gasket mounted on the doors. Since the metal sealing plate usually is larger than the magnetic gasket so as to ensure contact by the gasket upon closure of the door, a portion of the sealing plate usually extends beyond the gasket so as to be exposed to ambient air for prolonged periods even when the door is closed. Because of the high heat conductivity of the metal sealing plate, the portion of the sealing plate exposed to the ambient air often cools below the dew point temperature of the ambient air, again resulting in the undesired formation of condensation on such exposed portion.
Given the present problems with condensation and access to freezer interiors, the present invention utilizes an access tunnel that can be made at least partially from a thermal break extending from the interior of a freezer unit to the unit's exterior. This configuration reduces condensation build up and minimizes heating requirements of the sealing surface located at the sealed access door to the tunnel on the exterior of the freezer unit.
The present invention overcomes the prior art problems found with larger freezer access doors and frames by utilizing a less expensive, small access tunnel to retrieve freezer samples or contents. This access tunnel could be used in automation systems needing speedy access to freezer samples while minimizing ambient temperature introduction into the freezer's interior.